And don't forget, the angle of direction between you and the crow is important.

If you keep all this in mind, you can now develop a record of what calls proceed what events, and from this eventually derive a list of correlations.

If you are too lazy to do this, you could read Kakajarita ('Investigating the Cries of Crows') or, if you have trouble with Sanskrit, you could check out http://users.deltanet.com/~wcassidy/astro/crow.html
for a brief overview.